100 CHEMICAL ENGINEERING
effectively loaded, the capacity of any type of bucket elevator may be quite accurately ascertained by Formula (19).
W = Capacity in tons per hour, Z = Length of bucket in inches,
w = Width of bucket in inches,
V = Speed of elevator (buckets) in feet per minute,
w' = Weight of material handled in pounds per cubic foot, and
S = Spacing of buckets in inches.
Bucket-elevator equipment being balanced when not loaded, the power requirements consist in that required to lift the load, overcome the frictional resistance of the apparatus and that required to drag the buckets through the load collected in the elevator boot. The latter consumption of power is not great if the elevator is started before the feed to the boot, as the material is caught in the buckets as they rise in the boot.
Horsepower = , QQQ Formula (20)
W = Load handled in tons per hour, and
H — Height to which load is elevated in feet.
Standardization of bucket-elevator apparatus makes possible the derivation of a general equation for ascertaining the relative cost of such equipment with reasonable accuracy. Elevator buckets are usually either malleable iron or of steel, attached to one or two strands of ordinary detachable-link chain (engineering chain) or chain with malleable-iron links and steel pins (combination chain) or to high-grade rubber belts. Standard bucket elevators have buckets spaced 12, 15 or 18 in. Formula (21) for ascertaining the relative cost of standard elevators with any combination of buckets and chains may also be used for ascertaining the relative cost of continuous bucket elevators by simply substituting an interpolated value for the constant K, based on the depth of the V-bucket.
RCbe = F +Dwl Formula (21)
w = Width of bucket in inches, I = Length of bucket in inches, H — Height of elevator in feet,
wf =s Weight of material handled in pounds per cubic foot, K = Constant — 2.70, buckets spaced 12 in., = 2.17, buckets spaced 15 in., = 1 .80, buckets spaced 18 in., D = Factor varying inversely with size of bucket 2.1 to 1.1 for standard
steel buckets from 5 by 4 in. to 24 by 8 in. inclusive in size, and F = 1 . 78, malleable-iron buckets and combination chain, = 1.57, malleable-iron buckets and engineering chain, = 1.50, malleable-iron buckets and rubber belt, = 1 . 20, steel buckets and combination chain, = 1.00, steel buckets and engineering chain, = 0.92, steel buckets and rubber belt.